To place collect or credit card calls, you can reach AT&T Direct at 0800.99.00.11, or MCI WorldPhone by dialing 0800.99.00.19.
From a few hotels or homes, you may still be on a pulse dial system instead of DTMF ("touch tone"). You can still use your AT&T Direct or MCI card by dialing the number shown above, and waiting for the operator, but you won't be able to activate a voicemail service or answering machine. If you suspect this may happen to you, consider buying a small battery-operated touch-tone generator (available at Radio Shack, for instance) before leaving the U.S. In other cases, the hotel PBX is pulse-activated, but the central office accepts both pulses and tones. Sometimes, the phone handset will have a switch to change from pulse to tone, or the # key will activate touch-tones. In that case:
The direct dial sequence for the U.S. is 001+area code+number (the same as from anywhere in Europe, as a matter of fact). You can in general not reach toll-free numbers (800, 888, 877 or 866 area code) directly. You can call them through your calling card, but you will be billed for the call (there may be some exceptions).
Most phone booths in Paris are now operated with "stored value" smart cards rather than with coins; there is a drawing of a card on the side of the booth (the few remaining phone booths that take coins, usually in the countryside, have a drawing showing coins). The cards can be bought from the telephone counter in any post office, or from tobacconists. There are two different prices for the cards, about 7.50 euros for 50 message units, or 15 euros for 120 units. One unit gives you 3 minutes of talk for local calls during the day, and up to 9 minutes at night. For long-distance and international calls, the duration of the message unit is of course shorter. To use the phone card, lift the receiver, listen for the high-pitch tone, insert the card (face up, with the memory chip towards the telephone), close the lid over the card, wait for the dial tone, and dial. While talking, the phone's display will show you how many message units are left on the card. When you hang up, the lid will open after a couple of seconds to allow you to pull the card out. Cards are not refillable: when a card is used up, throw it away, or keep it as a collector item (they often have colorful advertising on them, and a whole collector network has sprung up).
You do not need a phone card to dial 0800 numbers.
At airports and in tourist areas, there are a few phones that take credit cards. Instructions are posted on these phones in multiple languages.
When calling a local number from a hotel, e.g., to dial up from your computer modem to your company or to an Internet Service Provider (ISP), note that even local calls are metered in France. Therefore those local calls can run your bill up -- expect to be paying about 15 cents a minute at hotel rates.